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United States Patent |
5,060,778
|
Daw
|
October 29, 1991
|
Moving coin validation
Abstract
A coin validation system includes a coin runway (1), a coil (2) positioned
adjacent to the runway and a resonant circuit (4) coupled to the coil (2).
A first signal monitoring circuit (6,8,12) is arranged to monitor
oscillating signals generated in the resonant circuit (4) as the coin
moves down the runway. The system further includes another coil (3). The
other coil (3) is displaced with respect to the one coil (2) in the
direction of movement of the coin (6) down the runway (1). Another
resonant circuit (5) is coupled to the other coil (3) and a second signal
monitoring circuit (7,8,11) are arranged to monitor the oscillating
signals generated in the other resonant circuit (5). The signal monitoring
circuits (6,7,8,11,12) are arranged to compare the signals in the resonant
circuits (4,5) and to determine from a measured signal parameter a
measurement which is representative of the coin (6) and which is velocity
and acceleration independent.
Inventors:
|
Daw; Ronald E. (Wimbourne, GB2)
|
Assignee:
|
Landis & Gyr Communications (GB2)
|
Appl. No.:
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403980 |
Filed:
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September 7, 1989 |
Foreign Application Priority Data
Current U.S. Class: |
194/317; 194/334 |
Intern'l Class: |
G07D 005/02; G07D 005/08 |
Field of Search: |
194/334,317,318,319
|
References Cited
U.S. Patent Documents
4124111 | Nov., 1978 | Hayashi | 194/334.
|
4462513 | Jul., 1984 | Dean et al. | 194/318.
|
4601380 | Jul., 1986 | Dean et al. | 194/318.
|
4660705 | Apr., 1987 | Kai et al. | 194/334.
|
4705154 | Nov., 1987 | Masho et al. | 194/334.
|
Primary Examiner: Bartuska; F. J.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
Claims
I claim:
1. A coin validation system comprising a coin runway, a first coil
positioned adjacent the runway, a first resonant circuit coupled to the
first coil, and first signal monitoring means arranged to monitor
oscillating signals generated in the resonant circuit as the coin moves
down the runway, characterized in that the system further includes a
second coil independent of the first coil, the second coil being displaced
with respect to the first coil in the direction of the movement of the
coin down the runway, a second resonant circuit independent of the first
resonant circuit and coupled to the second coil and second signal
monitoring means arranged to monitor oscillating signals generated in the
second resonant circuit, said first and second coils, said first and
second resonant circuits, and said first and second signal monitoring
means all operating concurrently, the first and second signal monitoring
means including means for comparing a signal in said first resonant
circuit and a concurrent signal in said second resonant circuit and
determining, from a measured signal parameter, a velocity and acceleration
independent measurement representative of the coin.
2. A coin validation system according to claim 1, in which the signal
monitoring means include processor means arranged to record successive
values of the frequencies of the signals in the two resonant circuits to
derive relative frequency curves for the two coils and to determine the
frequency at which the relative frequency curves intersect.
3. A coin validation system according to claim 2, in which each coil
comprises two half-coils, one on each side of the runway.
4. A coin validation system according to claim 3, in which the two
half-coils of each coil are connected in series.
5. A coin validation system according to claim 1, in which the two coils
have cores of similar dimension.
6. A coin validation system according to claim 1, in which the two coils
and their associated circuits are tuned to different frequencies.
7. A coin validation system according to claim 6, in which the signal
monitoring means are arranged to determine whether the coin is plated or
laminated by comparison of the signals at the different frequencies.
8. A coin validation system according to claim 6 or 7, in which the
different frequencies are substantially 100 KHz and 1 MHz.
9. A coin validation system according to claim 6, in which the outputs of
,the resonant circuits are divided in the ratio of their different
respective frequencies.
Description
The present invention relates to the validation of moving coins.
Coin validation apparatus is typically used in association with a coin
freed mechanism or a coin receiving machine such as a coin box telephone
or vending machine. Coin validation apparatus may also form part of a coin
sorting device to check that the coins are valid and not counterfeit.
It is known to detect properties of a coin for the purposes of validation
by measuring the effect of the coin on a coil in a tuned circuit In an
earlier design by the present applicants the coin is brought to rest
between two halves of a single tuned coil wound onto half cores of
ferrite. The coin partially obscures the two half coils from each other.
When it is positioned between the two half coils the coin increases the
resonant frequency of the coil both by reduction of the coils' positive
mutual inductance due to shielding and by the small resistance and
inductance of the coin being reflected into the coil by transformer
action. The magnitude of these effects depends principally upon the
overlap area of the coin and the coil. The coin is stopped at a fixed
reference point relative to the remainder of the validation apparatus and
its overlap with the coil then depends on its diameter. By measuring the
resonant frequency of the circuit the diameter of the coin is thus
determined and may be compared with a reference value to validate the
coin.
Static systems such as that described above suffer the disadvantage that it
takes a relatively long period of time to validate each coin since each
coin must be brought to rest, validated, and then urged in an appropriate
direction depending on the results of the validation. In order to mitigate
this disadvantage an arrangement described in EP-A-0203702 has been
developed to carry out measurements on a moving coin. In this system a
light beam detects the edge of a moving coin to initiate the measurement
of the frequency of the resonant circuit. Since frequency takes a finite
time to be measured the reading tends to be blurred by the movement of the
coin. This is compensated for by averaging two measurements, one made with
the coin moving into the coil and a second subsequent measurement made
with the coin moving out of the coil. Averaging the two readings in this
manner suffices to eliminate the effects of the coin's velocity, however
if the coin accelerates during its movement through the coil then the
change in velocity is not compensated for. Since in practice there is
always some variation in the velocity of the coin this gives rise to an
error which significantly limits the accuracy of the validation system.
According to the present invention a coin validation system comprising a
coin runway, a coil positioned adjacent the runway, a resonant circuit
coupled to the coil, and first signal monitoring means arranged to monitor
oscillating signals generated in the resonant circuit as the coin moves
down the runway, is characterised in that the system further includes
another coil, the other coil being displaced with respect to the one in
the direction of the movement of the coin down the runway, another
resonant circuit coupled to the other coil and second signal monitoring
means arranged to monitor oscillating signals generated in the other
resonant circuit, the first and second signal monitoring means being
arranged to compare the signals in the resonant circuits and to determine
from a measured signal parameter a velocity and acceleration independent
measurement representative of the coin.
Preferably the signal monitoring means include processor means arranged to
record successive values of the frequencies of the signals in the two
resonant circuits to derive relative frequency curves for the two coils
and to determine the frequency at which the relative frequency curves
intersect.
The present invention uses two spaced apart coils to provide an
instantaneous velocity and acceleration independent measurement of a
property of the coin being tested, such as its diameter. Each coil has its
own associated resonant circuit including an oscillator which generates an
oscillating signal By monitoring and comparing the signals in the two
resonant circuits it is possible to determine how far out of the upstream
coil the trailing edge of the coil is and how far into the downstream coil
the leading edge of the coin is Since the separation of the coils is fixed
and known it is then possible to compute a parameter dependent on the
diameter of the coin for the purpose of validation.
A system in accordance with the present invention is now described in
detail with reference to the accompanying drawings in which:
FIG. 1 is a block diagram of a coin validation system;
FIG. 2 is a circuit diagram showing a circuit suitable for use in the
system of FIG. 1; and
FIG. 3 is a graph showing normalised frequency curves for the two coils of
FIG. 1.
A coin validation system, which may be self contained or alternatively may
be incorporated into a larger system such as a pay telephone, includes a
coin runway 1 of conventional design In use a coin C is fed into the
runway 1 from a slot at its upper end and runs down the runway. Typically
at the lower end of the runway 1 there is provided a mechanism (not shown)
which switches the coin C between one or other of two paths in response to
an output signal from the validator.
Two coils 2,3 are positioned along the runway. Each coil comprises two
half-coils, one on each side of the runway. In the present example the two
half-coils are connected in series to each other and to a resonant circuit
4,5 including an oscillator which generates an oscillating signal. Other
arrangements are possible in which the two half-coils are connected in
parallel. Counters 6,7 connected to the resonant circuits 4,5 produce
outputs dependent upon the frequency of the signal in each resonant
circuit 4,5. The outputs of the counters 6,7 are fed to a microprocessor 8
which, in the manner described in further detail below, compares the
signal to determine a parameter dependent on the diameter of the coin and
compares the determined value with stored reference values. As a result of
this comparison the coin is determined to be valid or invalid and the
appropriate output signal produced.
As the coin C moves past each coil it changes the effective inductance of
the coil and so shifts the resonant frequency of the circuit of which the
coil forms a part. This effect and the construction of a suitable resonant
circuit and oscillator are described in greater detail in EP-A-0203702. As
the coin enters the upstream coil 2 the frequency of the oscillating
signal in the associated resonant circuit rises, reaching a maximum when
the coin is in the centre of the coil. Then as the coin moves further
forward the frequency of the oscillating signal in this circuit drops. At
the same time the coin moves into the downstream coil 3 and so the
frequency in the resonant circuit 5 begins to rise. This effect is shown
in FIG. 3 which is a plot of the normalised frequency of the resonant
signal in each resonant circuit against time. At time T.sub.c the relative
frequency curve for the first coil 2 which is falling from unity towards
zero intersects the relative frequency curve for the second coil 3 which
is rising from zero towards unity. At that time the coil is positioned
with its centre exactly midway between the two coils and from the
corresponding ordinate F.sub.c a parameter which scales with the diameter
of the coin may be determined. At this point the derivatives of the two
curves are equal and opposite.
The two coil cores are chosen to have similar dimensions and in the
preferred example are formed on circular ferrite cores. The two coils and
their associated circuits are tuned to different frequencies, in the
preferred example 100KHz and 1 MHz. The use of two frequencies optimises
the detection of non-homogeneous coins. The depth of penetration of the
coin by the field from the coil varies with frequency. It is therefore
possible by comparison of the response of the different coils at their
different respective frequencies to distinguish between, e.g., plated and
laminated coins. Dividing circuits are then provided between the output of
each resonant circuit and the associated counter to divide down the output
frequencies by the appropriate ratio. Thus in the present example the 100
KHz coil has its output divided by 10 and the 1 MHz coil has its output
divided by 100. However even after division the frequency curves of the
two coils will in general have different peak frequencies and different
minimum frequencies. The microprocessor 8 is therefore arranged initially
to shift the frequency curves to a common base line and to normalise the
curves so that they have a common amplitude. The microprocessor 8 stores a
number of readings, typically as many as 40 in a period of 250
microseconds as the coin passes the coils 2,3. From these numerous values
the relative frequency curves and the point of intersection of these
curves are determined. In this manner the crossover at time T.sub.c is
computed from a large number of points and so any random errors in the
measurements are eliminated. The microprocessor calculates from F.sub.c
the displacement of the trailing edge of the coin from the centre of the
upstream coil 2 and the distance of the leading edge of the coin from the
downstream coil 3. Since the separation of the coils 2,3 is known it is
then possible to calculate the diameter of the coin and to use this data
for validation of the coin by comparing the calculated value with stored
reference values. In practice the separation of the coils is chosen to be
such that the smallest coin to be tested has sufficient diameter to
overlap both coils and the largest coin to be tested is not so big that
both coils are covered simultaneously. The separation of the coils may be
determined precisely and the validator calibrated using tokens in the
manner described in EP-B-072 189.
FIG. 2 shows the oscillator and counter circuits in greater detail. The
amplitude of the oscillating signal in the oscillator circuit is monitored
via an integrating amplitude monitor 9 and feedback used to drive the
frequency of the oscillator so that it tracks the resonant frequency of
the circuit as it shifts as a result of the presence of the coin. FIG. 2
shows the oscillator circuit for a single coil: in practice this is
duplicated for the second coil.
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